1. Field of the Invention:
The present invention relates to an oil seal means of a rotary piston engine and, more particularly, to an oil seal means of a rotary piston engine wherein an oil seal ring which is mounted in an annular oil seal groove formed as a cut in a side wall portion of a rotor is provided with a resilient spring force which urges said ring outwardly from said oil seal groove thereby maintaining oil and gas tightness between the side wall of the rotor and a wall of a side or intermediate housing.
2. Description of the Prior Art:
A rotary piston engine has a general structure as exemplarly shown in FIG. 1, wherein a center housing 1 having a trochoidal inner surface is closed at its opposite ends by side or intermediate housings to define a chamber therein in which is mounted a polygonal rotor 4 which is adapted to make planetary movement around an eccentric shaft 3. While the rotor rotates in said chamber, the gas and oil tightness between a side wall of the rotor and an inner wall of the side housing 2 is maintained by an oil seal means generally designated by reference numeral 5. This oil seal means is conventionally composed of an annular oil seal groove formed as cut in the side wall of the rotor and an oil seal ring mounted in said groove, said oil seal ring being resiliently supported at its rear face by a corrugated spring or the like mounted between the rear face of the oil seal ring and a bottom wall of the annular oil seal groove so that the oil seal ring is urged outwardly from the annular oil seal groove and pushed against the wall surface of the side or intermediate housing at its front end portion in order to maintain oil and gas tightness at the contacting portion. Furthermore, a fluid passage which traverses an annular space left between the oil seal ring and wall portions of the annular oil seal groove is normally interrupted by an elastic O-ring.
In the conventional oil seal means of the aforementioned structure, if the oil and gas tightness at the contacting portion between the front end portion of the oil seal ring and the wall surface of the side or intermediate housing is to be maintained satisfactorily, the spring force for pressing the oil seal ring against the wall surface of the side or intermediate housing must be relatively strong. However, if this urging force is too strong it becomes difficult for the oil seal ring to follow the rotation of the rotor as it rotates, thereby causing the oil seal ring to slide circumferentially along the annular oil seal groove. If the circumferential sliding of the oil seal ring occurs in the annular oil seal groove, an elastic sealing member, such as an O-ring mounted between the annular oil seal groove and the oil seal ring, will suffer serious wear, resulting in detioration of its sealing performance within a short period of time. To overcome this problem, it has been proposed in the Laid Open Japanese Publication Sho 48-16204 to provide a notch at the rear face portion of the oil seal ring, said notch being engaged with an end portion of the corrugated spring which supports the rear face of the oil seal ring while the other end of said corrugated spring is engaged with a notch formed at a bottom wall portion of the annular oil seal groove. However, since the oil seal ring has to be resilient enough to follow, satisfactorily, a slightly concaved and convexed wall surface of the side or intermediate housing according to the rotation of the rotor, it is usually formed of a relatively thin member having a substantially U-shaped cross section which defines a concaved portion in which an O-ring is mounted. However, if an oil seal ring having a relatively thin cross section is provided with the aforementioned notch in a portion thereof, there is the problem that a crack might occur in said notch whereby breakage of the oil seal ring might result, especially during high speed operation of the rotor.